In the case of the known flowpacker the longitudinal edges of an initially flat film strip are brought together to form a tube around the articles moving in a stream with the film strip along a horizontal conveyor belt. The tube is closed in the lengthwise direction by joining together the longitudinal edges which have been brought together, thus forming a longitudinal fin. The tube is then pinched at regular intervals in transverse regions by means of so-called cross seal tools, and is sealed and cut through there in the transverse direction. Individual pouch-type packs are thus obtained from an initially flat film strip, each pouch being provided with a longitudinal seam and at each end a transverse seam, and the pouch containing one or more articles.
The cross seal tools are usually situated on two parallel cross seal shafts rotating in opposite directions, which shafts are disposed at a distance from each other on either side of the conveyor belt, and which run at right angles to the lengthwise direction of the conveyor belt. The cross seal tools project radially from the outer periphery of the rotating cross seal shafts. They are aligned in such a way that in each case two cross seal tools on either side of the conveyor belt touch each other so that they just overlap, and hold the film of the tube clamped between them. The speed of rotation of the cross seal shafts is usually synchronized with the speed of forward movement of the tube. If desired, the tube may be moved along intermittently through the pulling action of the rotating cross seal tools. Depending on the length of the pack to be made, which is determined by the distance between the transverse seams, and the diameter of the wrapper, which is determined by the contact faces of the cross seal tools, one or more cross seal tools are situated on a cross seal shaft, which tools are distributed at equal angular intervals over the radial periphery of the cross seal shaft. If the flowpacker needs to be reset, the number of cross seal tools per cross seal shaft and/or the distance between the contact face of the cross seal tools and the rotary shaft will also have to be adjusted, in order to adjust the distance between two successive transverse seams in the tube.
The cross seal tools have to meet high standards. They are designed to press the walls of the tube, which are made of relatively thin film, reliably against each other over the full width of the tube. At the same time, they have to ensure that the film parts which have been pressed against each other are bonded together. For this purpose, one or both cross seal tools are often heated, in order to heat-weld the film. Film which fuses together through sufficient pressure force is also sometimes used. Heating of the cross seal tools is not necessary in that case. It will be clear that in both cases only an extremely slight variation is permissible in the pressure force produced by the cross seal tools over the width of the transverse seam. The cross seal tools are also generally provided with cutters, in order to cut through the tube in the transverse seam regions. The operation of the cutters must be sufficiently reliable over the full width of the transverse seam region. If the welding and/or cutting off is not sufficiently reliable, this will lead to considerable production problems, which are inadmissible, in view of the high production speeds - several hundred packs per minute. It will be clear that this means high standards being set for the adjustment of the cross seal tools, the rotary shafts on which they are situated, and the support and drive of said shafts. It is for those reasons that the rotary shafts are mainly bilaterally supported.
It is already known to support and drive the cross seal tools unilaterally, which means that the accessibility of the conveyor belt in the area around the cross seal tools is increased compared with bilaterally supported cross seal shafts. This means that, for example, adjustment operations on the cross seal tools fixed on the cross seal shafts are simpler, and cleaning and maintenance of the flowpacker is simpler and easier to carry out.
However, given the required accuracy of the operation of the cross seal tools mentioned above, the use of unilaterally supported rotary shafts for the cross seal tools requires special design measures. In particular, account has to be taken of sagging of the rotary cross seal shafts from the support towards the free, unsupported axial end. As a result of this, removal of the cross seal shaft for resetting the flowpacker by adjusting the cross seal tools is virtually impossible.
Therefore, as far as unilaterally supported cross seal shafts are concerned, it is common practice to fit the cross seal tools on the cross seal shaft in such a way that they can be removed separately. In this case it is usual only to connect each cross seal tool to the cross seal shaft by means of one or more bolts projecting radially into the cross seal shaft. In the holes pattern in the cross seal shaft account is taken of the possibility of fitting various numbers of cross seal tools distributed at equal angular intervals. It is thus possible in turn to fit, for example, one, two or four or, for example, one, three or six cross seal tools on one cross seal shaft. In the holes pattern account can even be taken of the possibility of alternately using three or four cross seal tools. It will be clear that a complicated holes pattern in the cross seal shaft is necessary for such a possibility. Consequently, problems arise, such as space problems for the bolt shanks projecting into the cross seal shafts, the bolts connecting the cross seal tools to the cross seal shafts are difficult to reach for fitting and removal, and special equipment is consequently required, and the extensive holes pattern considerably weakens the cross seal shaft and consequently makes it more flexible, with the result that the sagging of the cross seal shaft increases, which has an adverse effect on reliable operation of the cross seal tools over the total transverse length of the tube. In practice, account is therefore taken mainly of the possibility of doubling or halving the number of cross seal tools on a cross seal shaft. For a different setting, such as the changeover from three to four tools, replacement of a complete cross seal shaft is necessary, with all the adjustment problems which this entails.
The known system for changing the cross seal tools on unilaterally supported cross seal shafts therefore still has disadvantages. For example, the necessary resetting operations are still major operations, since in each case the cross seal tools have to be fitted and removed and adjusted to the cross seal shaft one by one, which involves a considerable idle period for the flowpacker. On the other hand, the required holes pattern causes an unavoidable reduction in the bending rigidity of the cross seal shaft, which reduces the functioning reliability. Despite those disadvantages, the known system has already been in use for quite a long time.
Recapitulating, for quite a long time there has been a desire for a more practical system of changing the cross seal tools on the unilaterally supported cross seal shafts of a flowpacker, for purposes of resetting operations, but also for maintenance work, bearing in mind the requirements for accurate working of the cross seal tools.